Rhabdomyolysis (Rhabdo)

What happens in rhabdomyolysis

When muscle cells are damaged, their contents leak into the bloodstream:

• Myoglobin: an oxygen-carrying protein that is filtered by the kidneys. In large amounts it turns urine dark and can block and damage kidney tubules, causing acute kidney injury.
• Potassium: high levels (hyperkalemia) can cause dangerous heart rhythms.
• Creatine kinase (CK): a muscle enzyme used to diagnose and track the condition.
• Phosphate, uric acid and acids, which add to kidney and metabolic problems.

Fluid also moves into injured muscle, causing swelling, dehydration and sometimes compartment syndrome.

Causes

Physical causes

• Extreme or unaccustomed exercise, especially high-repetition workouts such as spin classes, CrossFit, military training or marathon running, particularly in the heat, when dehydrated or untrained
• Crush injuries from accidents, earthquakes or building collapse
• Prolonged immobility: lying on the floor after a fall, stroke, overdose or intoxication
• Heat stroke and high body temperature
• Seizures, severe agitation, electrical injuries and lightning strikes
• Lack of blood flow to a limb, such as a blocked artery

Drugs, toxins and medicines

• Alcohol, especially binge drinking
• Cocaine, amphetamines, MDMA and other stimulants
• Statins (rare, higher risk with high doses or interacting medicines). See statin-induced myopathy
• Antipsychotics (neuroleptic malignant syndrome), anesthesia (malignant hyperthermia)
• Snake and insect venoms, carbon monoxide

Other causes

• Infections: influenza, COVID-19, other viruses and severe bacterial infections
• Electrolyte imbalances: low potassium or phosphate
• Thyroid disease and uncontrolled diabetes
• Inherited muscle disorders, such as McArdle disease and other metabolic myopathies, which cause recurrent episodes with exercise

Symptoms

• Muscle pain, tenderness and aching, often in the thighs, calves, shoulders or lower back
• Muscle weakness or difficulty moving
• Swollen muscles
• Dark red, brown or cola-colored urine
• Reduced urine output
• Tiredness, nausea, vomiting
• Fever, confusion and a fast heart rate in severe cases

Some people have no muscle pain and the diagnosis is found only on blood tests.

Diagnosis

• Creatine kinase (CK): usually more than 5 times the upper limit of normal, often thousands or tens of thousands of units per liter. CK peaks 1 to 3 days after injury.
• Urine tests: a dipstick positive for blood but with few red blood cells under the microscope suggests myoglobin.
• Kidney function, potassium, calcium and phosphate blood tests.
• ECG if potassium is high.
• Tests for the cause: drug screen, thyroid tests, infection tests, and genetic or muscle testing for recurrent episodes.

Treatment

• IV fluids: large volumes of fluid started early to flush myoglobin through the kidneys. Urine output is closely monitored.
• Treating high potassium and other electrolyte problems.
• Stopping causative medicines or drugs.
• Treating the cause: cooling for heat stroke, managing seizures, treating infection.
• Dialysis for severe kidney failure, dangerous potassium or fluid overload. It is usually temporary.
• Fasciotomy: surgery to relieve pressure if compartment syndrome develops.

Mild exertional rhabdomyolysis in a healthy person with normal kidney function can sometimes be managed with oral fluids and close follow-up, but this decision should be made by a clinician.

Recovery and returning to exercise

Most people recover fully, especially with early treatment. Kidney function usually returns to normal over weeks if it was affected. After exertional rhabdomyolysis, return to exercise gradually over weeks once CK and symptoms have normalized, guided by your doctor. Recurrent episodes should prompt testing for an underlying muscle disorder.

Prevention

• Build up exercise intensity gradually, especially with new high-intensity programs.
• Stay well hydrated and avoid strenuous exercise in extreme heat.
• Do not exercise through severe muscle pain.
• Avoid alcohol binges and stimulant drugs.
• Tell your doctor about unexplained muscle pain while taking statins.
• Check on vulnerable people who live alone, as long periods on the floor after a fall are a common cause.

Frequently asked questions

What are the first signs of rhabdomyolysis?

Early signs include muscle pain and weakness out of proportion to activity, muscle swelling, and dark tea- or cola-colored urine. Some people feel tired or nauseated. Dark urine with muscle pain after hard exercise, injury or heat exposure needs emergency care.

What causes rhabdomyolysis?

Common causes include extreme or unaccustomed exercise, crush injuries, lying immobile for long periods, heat stroke, alcohol and drugs such as cocaine, certain medicines including statins, seizures, infections and inherited muscle disorders.

Can you recover from rhabdomyolysis?

Yes, most people recover fully, especially when treated early with IV fluids. Muscle soreness improves over days to weeks. If the kidneys were affected, they usually recover, though a small number of people need temporary dialysis or have lasting kidney damage.

How is rhabdomyolysis different from normal muscle soreness?

Normal post-exercise soreness peaks 1 to 3 days after exercise and steadily improves, with normal urine. Rhabdomyolysis causes more severe pain, swelling and weakness, and often dark urine. Blood tests show very high CK levels. If in doubt, get checked.